Grantee Research Project Results

Final Report: Three-Phase Ammonia Air Scrubber Recycles Water

EPA Grant Number: SU836779
Title: Three-Phase Ammonia Air Scrubber Recycles Water
Investigators: Barsanti, Kelley , Tam, Kawai , Collado, Joanna , Ross, Kayla , Turner, Taylor , Zendejas, David , Lichtenberg, William
Institution: University of California - Riverside
EPA Project Officer: Page, Angela
Phase: I
Project Period: October 1, 2016 through September 30, 2017 (Extended to September 30, 2018)
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2016) RFA Text |  Recipients Lists
Research Category: Sustainable and Healthy Communities , P3 Awards , P3 Challenge Area - Safe and Sustainable Water Resources

Objective:

Agricultural producers are primary contributors to atmospheric ammonia pollution throughout the United States. California in particular, as the leading state in cash farm receipts, contributes significantly more ammonia emissions than any other U.S. state; with the largest contribution coming from dairy facilities. In 2000, the Air Quality Management District (AQMD) reported, “Most of the potentially significant sources of ammonia are area-wide sources such as livestock, fertilizer application, and soils.”[1] Although ammonia is not a federal hazardous air pollutant or a state-identified toxic air contaminant, its acute and chronic non-cancer health effects justify its regulation under the AQMD’s risk management programs. The risk of ammonia pollution is attributed to its ability to react with other contaminants in the air to produce fine particulate matter (PM2.5), which enters the human respiratory system and can cause significant health issues.

Modern agricultural producers use chemical scrubbers to reduce ammonia emissions. These scrubbers use significant amounts of water, as the scrubbers are flushed continuously to avoid clogging. Our primary sustainability challenge is to reduce the calculated water consumption of 158,900 gpd (gallons per day) without compromising performance. Our secondary sustainability challenge is to maximize the separation efficiency of ammonia from both the initial air (feed gas) and flushing water stream. We have designed a three-step ammonia air scrubbing and filtration system that promotes sustainability by reusing water, recycling waste, and reducing costs. While ammonia emissions from agricultural sources remain a significant concern for air quality, the current conventional chemical scrubbers do not represent a sustainable solution, as they have high economic and environmental costs. “Non-chemical” water scrubbers do exist, but they are not sustainable with respect to ammonia removal because a continual stream of water is required, adding economic and environmental costs. Our innovative three-step design builds on these current systems to facilitate eventual large-scale adoption. Step one uses a water-based air-scrubbing (gas absorbing) unit. Step two uses a novel manure-based biochar adsorption column to collect ammonium from the waste stream, cleaning the water for reuse. This second step eliminates the requirement for waste disposal of the water-ammonium effluent. Step three uses an air stripper to further reduce the ammonia concentration from the water. At the end of the three-step system the water can be reused to complete the cycle again. In P3 Phase I of this project we tested the biochar adsorbent; in P3 Phase II of this project we will build and test a field-scale version of our three- step system, which has great potential for reducing economic and environmental costs.

P3 Phase I one of this project focused on optimizing the design of our three-step air- scrubbing system and conducting bench-scale experiments of the biochar adsorption step. Optimization design goals were: meeting air quality needs and complying with statewide mandates to cut water usage, while reducing generated waste and overall costs. The introduction of water recycling in this three-step air-scrubbing system will significantly reduce the 158,900 gpd calculated for a current system. With four consecutive years of drought, water conservation efforts are imperative in California. In May 2015, ABC Channel 7 news reported that “the Inland Empire, Riverside County had to do as much as 25 to 30 percent” in water reduction to keep up with mandates. [2] Outcomes of this project include: less air pollution due to ammonia and less ammonium containing waste effluent; reduction of costs allocated to water consumption and for water treatment; and less money lost due to devalued areas based on lack of water supplies.

Summary/Accomplishments (Outputs/Outcomes):

The outputs and outcomes focused on three components: design of the biochar adsorption column, effectiveness of ammonia removal through the adsorption column, and an economic assessment of the complete system. The design for the first two-steps of the three-step air-scrubber was based on the available spacing at Scott Brothers Dairy facility in Moreno Valley, CA (location for P3 Phase II field test, see letter). The facility currently encompasses 400 acres including an on- site wastewater treatment facility. The design specifications for the adsorption column allow for an ammonia input of 25g NH3/hr to accommodate the average ammonia emissions during the months of March to September, when ambient temperatures are at a maximum.

During P3 Phase I, a bench-scale prototype of the second step (adsorber) was constructed and used to conduct experiments to evaluate the ammonia removal efficiency. A one gram biochar sample was used in the prototype. The results from the bench-scale experiments demonstrate a 67% removal efficiency. This achievement surpassed the predicted 55% removal efficiency SuperPro (mathematical model). For our P3 Phase II, it was determined that a 10ft column with a bed depth of 6ft would achieve the same ammonia removal efficiency (67%) as achieved with the bench-scale prototype.

The Scott Brothers Dairy currently does not have an ammonia reduction system in place, thus the reduction in ammonia emissions would provide an economic benefit to Scott Brothers Dairy (and ultimately other facilities) as listed in Table 1. The AQMD has a threshold of 200lbs of ammonia per year, fees are imposed on emissions above the 200lbs per year. Based on AQMD emission factors, the 2100 cows at the Dairy emit a total of 51lb of ammonia per cow per year.[3] At a cost of $0.03/lb, the Dairy currently pays an annual fee of $3,207. Based on design calculations and the bench-scale lab results, our three-step scrubber system will remove 70% of the gas-phase ammonia by absorption to water stream; the biochar adsorption then removes 67% of the aqueous ammonium, yielding a 53% reduction in total ammonia emitted. This 53% reduction in emissions would system save the Dairy $1504 in AQMD fees per year.

Conclusions:

Overall, we achieved an ammonia removal efficiency of 67%, surpassing the modeled 55% based on the average ammonia concentration using the minimum amount of water required. While the efficiency was reasonable, the results were obtained in a laboratory environment with a single biochar sample with limited variations in particle size and can be improved upon. We hypothesize that biochar samples with smaller particle sizes will allow for higher removal efficiency due to an increase in surface contact area. Nonetheless, the relatively high removal efficiency achieved demonstrates that the second step design is an effective and environmentally contributive method for removing ammonia from dairy operations. This is the most important of the three steps for achieving sustainability goals and the success of this step supports moving on to a field-scale version of the our three-step air-scrubber system. Our innovative design will satisfy the overarching goal of preventing large emissions of ammonia into the atmosphere which contribute to pollution-induced health risks; while also significantly reducing the water consumption of agricultural operations in comparison to existing ammonia removal methods.

Proposed Phase II Objectives and Strategies

A complete installation of our design, which includes the initial absorber unit, complete biochar adsorption column, the water-based air stripper, and relevant input and output systems will be constructed and tested at the Scott Brothers Dairy facility over the span of two years. The adsorption column will be constructed using the design dimensions established in P3 Phase I. Scott Brothers Dairy will provide an allotted area for installation of our proposed system. The team will continue to examine the effectiveness of biochar as an adsorbent in this system and address any concerns that arise. Additionally, further laboratory research will be conducted in P3 Phase II to examine and improve the adsorption capacity of the biochar through advanced particle sieving techniques to achieve finer material for more adsorption. More accurate instrumentation, an advanced ammonia analyzer, will be used in the laboratory and in the field. 

Upon the implementation of our design at the Dairy, on-site emissions will be reduced and the facility will be supporting and demonstrating a sustainable approach to treating ammonia emissions while also achieving water savings and effluent reduction. We will monitor the ammonia emissions produced by the facility throughout the year to ensure the productivity of the design. We will also monitor any potential “unintended” effluent (spent biochar, non-recyclable water, etc.). Moreover, we will meet with the dairy facility employees and surrounding community members to address any concerns they may have or suggestions for improvement.

Journal Articles:

No journal articles submitted with this report: View all 1 publications for this project

Supplemental Keywords:

Ammonia mitigation, water conservation, water purification, agricultural pollution, biochar filtration

Progress and Final Reports:

Original Abstract

2017 Progress Report

P3 Phase II:

Three- Step Scrubber for Ammonia Removal  | 2018 Progress Report  | 2019 Progress Report  | 2020 Progress Report  | 2021 Progress Report  | 2022 Progress Report  | 2023 Progress Report